1. Field:
The present invention relates to air purifiers and, more particularly, to purifiers of the centrifugal filtration type incorporating an ionization feature and the method for removing particulates from contaminated air.
2. Prior Art:
Prior art apparatus is represented by the structure of U.S. Pat. No. 3,538,657 to L. Macrow that describes a gas-liquid contact apparatus wherein there are two separate gas-liquid stages. U.S. Pat. No. 3,544,084 to L. Macrow also describes an improved gas-liquid contact apparatus for effective mixing between a gas and a liquid without appreciable entraining the liquid in the gas, and without experiencing a substantial pressure drop in the gas passing through the apparatus.
Prior art apparatus that purifies contaminated air or gas streams direct the air through a rapidly rotating filtration element made of nylon threads. Fine particles of oil mist encountering the revolving nylon threads are trapped in the capillary structure of the threads and, under the influence of centrifugal force, flow to the outer periphery of the element and are thrown off into the housing around the element.
It was found that this system operated with high collection efficiency for droplets of relatively large size, that is, in excess of 2 or 3 microns diameter. But particles of much smaller size, that is, down to submicron size, were of such small mass that they could not be impacted on the rotating threads, and passed through the rotating element along with the air stream. Thus, the prior art apparatus was capable of achieving 98% to 99% collection efficiency by weight, if the particulates being collected were principally of large size, that is, in excess of 2 or 3 microns. However, if the major portion of the particulates were in the range of less than 2 or 3 microns and down into the submicron range, a much larger percentage by weight would pass through the element, thus materially reducing its collection efficiency by weight, on predominantly small particulate.
To improve overall efficiency under these conditions, a two-stage unit was made available, which added a bank of electrostatic filters on the discharge of the centrifugal filtration element. The second stage than collected the small particulate which had passed through the first stage, at a relatively high efficiency, which is typical of the electrostatic filter on small particulate. Thus, the two-stage unit produced a high combined efficiency due to the high basic efficiency of the centrifugal filtration element on large particulate, and the high basic efficiency of the electrostatic unit on small particulate.
However, the two-stage unit was bulky and costly.
The present invention for ionization of small particulate overcomes the weaknesses of previous wire-type ionizers. In general, these consist of fine wires carrying the ionizing voltage, which are stretched across the incoming dirty air stream. Streams of ions emit from the fine ionizer wire across the air stream. However, the fine ionizer wire tends to coat itself with impurities from the air stream, forming an uneven coating on the wire and, at points where this occurs, it prevents the emission of ions. Thus, after prolonged operation of the system, ionization is no longer uniform along the length of the ionizer wire and the ionizing field is broken up into stratified layers. Thus, some particles pass through the ionizer without becoming ionized and consequently are not collected and the efficiency of collection drops. It is then necessary to totally clean the ionizer wire by removing the coating with abrasives or chemicals to restore a totally clean surface which will then generate uniform ion flow. While the problem of keeping ionizers clean vaires with the severity of the application, it is nevertheless a difficult and time consuming operation, which, if not timely performed, results in deterioration of the equipment as well as performance. This comes about because, when ionizer wires become coated, preventing normal ionization, voltage in the circuit rises to an abnormally high level causing arcing at other points in the collector cell or powerpack components.